The present invention relates to a wireless handset, particularly to a wireless handset mounted with independent antennas for transmission and for receiving preferable for a wireless handset used in a communication system in which different frequencies for transmission and for receiving are simultaneously used.
Currently and generally, according to a wireless handset used in a communication system in which different frequencies for transmission and for receiving are simultaneously used, in order to carry out transmission and receiving by a single antenna, there is provided a duplexer between a transmission system circuit and a receiving system circuit and an antenna such that a transmitted signal is directed to the antenna but is not directed to the receiving system circuit and a received signal is directed from the antenna to the receiving system circuit but is not directed to the transmission system circuit. According to such a constitution constructed by the antenna, the duplexer and the transmission/receiving systems, transmission power is lost in the transmission system and minimum receiving power sensitivity is restricted in the receiving system by insertion loss of the duplexer. Loss of passband is increased when an attenuation amount of stopband is intended to sufficiently ensure in a communication system having a wide transmission and receiving bandwidth, particularly a communication system in which frequency interval for transmission and receiving is near, that is, a frequency interval of passband and stopband in a transmission or receiving filter of the duplexer is near. Loss of transmission power in a wireless handset gives rise to a need of ensuring extra battery capacity and hampers downsized formation necessary for the wireless handset. Further, loss of receiving power deteriorates the minimum receiving power sensitivity and hampers promotion of function of wireless device.
Hence, according to a conventional wireless handset, there is proposed a constitution in which independent narrow band antennas are provided respectively for a transmission and a receiving system, the antennas are directly connected to a transmission system circuit and a receiving system circuit to thereby enable to downsize the handset and promote its function in Japanese Patent Laid-open (Kokai) No. Hei 11-251948. An example of the constitution is shown by FIG. 13.
In FIG. 13, numeral 200 designates a circuit board of a wireless handset and numerals 210 and 220 designate a transmission system circuit and a receiving system circuit respectively provided on the circuit board 200. A transmitted signal generated by the transmission system circuit 210 is radiated to space from a built-in antenna 160 in which only transmission frequency band constitutes passband via a radio frequency (RF) filter for transmission 301. A signal to be received in space is caught by a helical antenna 170 in which only receiving frequency band constitutes passband when an exterior antenna is contained and is transmitted from an exterior antenna electricity feed point 172 above the circuit board 200 connected to an electricity feed point 171 of the helical antenna to the receiving system circuit 220 via a receiving radio frequency (RF) filter 302. When the exterior antenna is extended, by connecting the exterior antenna electricity feed point 172 to an electricity feed point 174 of a monopole antenna 173 in which only the receiving frequency band constitutes passband, a signal caught by the monopole antenna 173 is transmitted to the receiving system circuit 220.
According to the constitution, the built-in antenna 160 and the helical antenna 170 or the monopole antenna 173 which is the exterior antenna are constructed by constitutions of narrow band. That is, gain is low at a received frequency in the antenna for transmission and sensitivity is low at a transmitted frequency in the antenna for receiving and accordingly, an attenuation amount at stopband is not so much needed in the radio frequency (RF) filters 301 or 302 provided between the antennas and the transmission system circuit 210 or the receiving system circuit 220. In the case of a filter in which the attenuation amount at stopband is not so much needed, the insertion loss can be restrained low. Therefore, the wireless handset according to the constitution realizes downsized formation by reducing battery capacity by reducing loss of transmission power and realizes promotion of the minimum receiving power sensitivity by reducing loss of receiving power.
According to the conventional wireless handset proposed in Japanese Patent Laid-open (Kokai) No. Hei 11-251948, the transmission and receiving antennas are respectively constructed by the constitutions in narrow band and accordingly, the attenuation amounts at stopband of the radio frequency (RF) filters respectively for transmission and receiving provided respectively between the transmission and receiving antennas and the transmission and receiving circuits may be restrained low. However, even the antenna of narrow band is provided with more or less sensitivity in near frequency band and accordingly, there poses a problem in a communication system in which frequency intervals for transmission and receiving are near to each other, in which the antenna for transmission is provided with more or less sensitivity in receiving band and the antenna for receiving is provided with more or less sensitivity in transmission band, the attenuation amount of stopband of the radio frequency (RF) filter cannot be restrained low in the conventional constitution of the wireless handset and accordingly, the insertion loss cannot be reduced.
It is an object of the present invention to provide a novel wireless handset achieving downsized formation and promotion of function by using independent antennas for transmission and receiving and restraining interference between the transmission and receiving antennas in a communication system in which different and near frequencies for transmission and for receiving are simultaneously used.
The above-described problem of the present invention can effectively be resolved by providing a magnetic current antenna for transmission and a magnetic current antenna for receiving arranged in parallel with each other such that respective magnetic currents are disposed on a straight line in a wireless handset used in a communication system in which different frequencies for transmission and for receiving are simultaneously used.
A plurality of magnetic current antennas can mostly reduce interference among magnetic antennas when the antennas are arranged such that magnetic currents are aligned in a straight line and accordingly, when the magnetic current antennas for transmission and for receiving are arranged in parallel with each other such that respective magnetic currents are disposed on a straight line, interference among the antennas for transmission and for receiving is minimized and there can be reduced signal leakage from a radio frequency circuit for transmission to a radio frequency circuit for receiving which becomes problematic in a wireless handset simultaneously carrying out transmission and receiving. When the signal leakage among the radio frequency circuits for transmission and for receiving is small, there can be reduced attenuation amounts of stopband in radio frequency filters respectively provided between the antennas for transmission and for receiving and the transmission and receiving circuits. Generally, a radio frequency filter having a small attenuation amount of stopband can be fabricated with small loss of passband. Therefore, by adopting such a means, a wireless handset can be downsized by reducing battery capacity since power loss in transmission is reduced and minimum receiving power sensitivity function of a wireless handset can be promoted since power loss of receiving can be reduced.
Further, the above-described problem of the present invention can effectively be resolved by providing antennas, a control circuit for changing central frequencies of impedance matching of the antennas and band-switching filter circuits which are connected to the antennas and bands of which are switched by the control circuit.
In a communication system, bandwidth used for operation is generally narrower than bandwidth of a total of a system. Therefore, by changing central frequency of impedance matching of an antenna in compliance with operating frequency, an antenna having narrow bandwidth can be used. Generally, bandwidth of an antenna is proportional to a volume thereof and accordingly, an antenna having narrow bandwidth can be realized in a small size. Similarly, by switching band of a filter in compliance with operating frequency, a filter having narrow bandwidth can be used. When passband is not extremely narrower than used frequency, generally, a filter having narrow bandwidth can be realized such that insertion loss is smaller than that of a filter having wide bandwidth. Therefore, by adopting such a means, a small-sized antenna and a filter having small insertion loss can be used by simultaneously controlling the antenna and the filter by a common control circuit and accordingly, the sensitivity for receiving can be promoted while further downsizing a wireless handset.
Further, according to a wireless handset which has an antenna for transmission and an antenna for receiving and in which directions of main polarization of the antenna for transmission and the antenna for receiving are the same, insertion loss of radio frequency filters respectively provided between the antennas for transmission and receiving and transmission and receiving circuits can be reduced, further, directions of main polarization of the antennas for transmission and receiving can be aligned to a direction of polarization used in a system in which the wireless handset is used and accordingly, transmission and receiving can be carried out efficiently.